Commit | Line | Data |
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2c5ff4e4 | 1 | /* |
ab5be9fa | 2 | * Copyright (C) 2019 Jérémie Galarneau <jeremie.galarneau@efficios.com> |
2c5ff4e4 | 3 | * |
ab5be9fa | 4 | * SPDX-License-Identifier: GPL-2.0-only |
2c5ff4e4 | 5 | * |
2c5ff4e4 JG |
6 | */ |
7 | ||
8 | #ifndef LTTNG_OPTIONAL_H | |
9 | #define LTTNG_OPTIONAL_H | |
10 | ||
11 | #include <stdint.h> | |
2c5ff4e4 JG |
12 | |
13 | /* | |
14 | * Define wrapper structure representing an optional value. | |
15 | * | |
16 | * This macro defines an "is_set" boolean field that must be checked | |
17 | * when accessing the optional field. This "is_set" field provides | |
18 | * the semantics that would be expected of a typical "raw pointer" field | |
19 | * which would be checked for NULL. | |
20 | * | |
21 | * Prefer using this macro where "special" values would be used, e.g. | |
22 | * -1ULL for uint64_t types. | |
23 | * | |
2c5ff4e4 JG |
24 | * Declaration example: |
25 | * struct my_struct { | |
26 | * int a; | |
8250d597 | 27 | * LTTNG_OPTIONAL(int) b; |
2c5ff4e4 JG |
28 | * }; |
29 | * | |
30 | * Usage example: | |
31 | * struct my_struct foo = LTTNG_OPTIONAL_INIT; | |
32 | * | |
33 | * LTTNG_OPTIONAL_SET(&foo.b, 42); | |
34 | * if (foo.b.is_set) { | |
35 | * printf("%d", foo.b.value); | |
36 | * } | |
37 | * | |
38 | * LTTNG_OPTIONAL_UNSET(&foo.b); | |
39 | */ | |
40 | #define LTTNG_OPTIONAL(type) \ | |
41 | struct { \ | |
42 | uint8_t is_set; \ | |
43 | type value; \ | |
44 | } | |
45 | ||
0a30bf9b JG |
46 | /* |
47 | * Alias used for communication structures. If the layout of an LTTNG_OPTIONAL | |
48 | * is changed, the original layout should still be used for communication | |
49 | * purposes. | |
50 | * | |
51 | * LTTNG_OPTIONAL_COMM should be combined with the LTTNG_PACKED macro when | |
52 | * used for IPC / network communication. | |
53 | */ | |
54 | #define LTTNG_OPTIONAL_COMM LTTNG_OPTIONAL | |
55 | ||
2c5ff4e4 JG |
56 | /* |
57 | * This macro is available as a 'convenience' to allow sites that assume | |
a0377dfe | 58 | * an optional value is set to LTTNG_ASSERT() that it is set when accessing it. |
2c5ff4e4 JG |
59 | * |
60 | * Since this returns the 'optional' by value, it is not suitable for all | |
61 | * wrapped optional types. It is meant to be used with PODs. | |
62 | */ | |
63 | #define LTTNG_OPTIONAL_GET(optional) \ | |
a321667a | 64 | ({ \ |
a0377dfe | 65 | LTTNG_ASSERT((optional).is_set); \ |
bc2dc8d4 | 66 | (optional).value; \ |
2c5ff4e4 JG |
67 | }) |
68 | ||
3da864a9 JR |
69 | /* |
70 | * This macro is available as a 'convenience' to allow sites that assume | |
a0377dfe | 71 | * an optional value is set to LTTNG_ASSERT() that it is set when fecthing the |
3da864a9 JR |
72 | * underlying value's address. |
73 | */ | |
74 | #define LTTNG_OPTIONAL_GET_PTR(optional) \ | |
75 | ({ \ | |
a0377dfe | 76 | LTTNG_ASSERT((optional).is_set); \ |
3da864a9 JR |
77 | &(optional).value; \ |
78 | }) | |
79 | ||
2c5ff4e4 | 80 | /* |
5747e45a | 81 | * Initialize an optional field as unset. |
2c5ff4e4 JG |
82 | * |
83 | * The wrapped field is set to the value it would gave if it had static storage | |
84 | * duration. | |
85 | */ | |
1c9a0b0e | 86 | #define LTTNG_OPTIONAL_INIT_UNSET {} |
5747e45a JG |
87 | |
88 | /* | |
89 | * Initialize an optional field as 'set' with a given value. | |
90 | */ | |
7966af57 | 91 | #define LTTNG_OPTIONAL_INIT_VALUE(val) { .is_set = 1, .value = val } |
2c5ff4e4 JG |
92 | |
93 | /* Set the value of an optional field. */ | |
bc2dc8d4 MD |
94 | #define LTTNG_OPTIONAL_SET(field_ptr, val) \ |
95 | do { \ | |
bc2dc8d4 | 96 | (field_ptr)->is_set = 1; \ |
7966af57 | 97 | (field_ptr)->value = (val); \ |
bc2dc8d4 | 98 | } while (0) |
2c5ff4e4 JG |
99 | |
100 | /* Put an optional field in the "unset" (NULL-ed) state. */ | |
bc2dc8d4 MD |
101 | #define LTTNG_OPTIONAL_UNSET(field_ptr) \ |
102 | do { \ | |
103 | (field_ptr)->is_set = 0; \ | |
104 | } while (0) | |
2c5ff4e4 JG |
105 | |
106 | #endif /* LTTNG_OPTIONAL_H */ |